1. Field of the Invention
The present invention relates to a circuit breaker generally, and more particularly, to the provision of an improved interrupter for extinguishing an arc in a circuit breaker utilizing a pressurized fluid as an interrupting medium, such as sulfur hexafluoride SF.sub.6 gas for example.
2. Description of the Prior Art
For better understanding of the nature and objects of the invention, reference may be had to the following description of the prior gas blast circuit breakers.
In an interrupter for use with a pressurized interrupting fluid, the fluid itself is required to have an excellent arc quenching capability without question, but also blasting the fluid toward the arc so as to dissipate arcing energy and cool down the temperature around the arc is considered to be an effective means to improve the arc quenching capability.
To furnish a strong blasting flow of fluid, a means to provide a pressure difference between the two extreme ends of the arcing space is required. In the conventional gas blast circuit breakers, this is accomplished by way of two provisions, one, a puffer type interrupter which comprises a puffer system interlocked with opening and closing operation of contact members of a circuit breaker and the other, a dual pressure type interrupter which comprises a gas compressor providing a high pressure to be discharged through valves interlocked with opening and closing operation. In these systems, however, various problems have been found as shown below. To operate the puffer system mechanically in conjunction with opening and closing operations, a considerably large actuating power is required.
The actuating power required increases with an increase in arcing currents, this in turn makes the puffer system large in size and consequently, its mechanism transmitting operating power is required to be highly rigid. During the no load period which ranges a large portion of the puffer system operation and when the interrupter is closing and opening a small current flow, the puffer system provided with a large operating capacity (for large current interruption) will operate with an excess power that drives the puffer mechanism too fast for a small current being interrupted. This tendency becomes more pronounced as the capacity of a circuit breaker increases, causing a split off of current and abnormal voltage rise. In the dual pressure type interrupter, because of its dual pressure line configuration and required equipment supporting its operation like the valves, compressor and control devices, the whole system becomes large in size and complicated.
To eliminate the disadvantages of heavy cost and complicated structure in these conventional systems, a new type gas blast circuit breaker, simple in structure and economical, has been recently developed. This circuit breaker comprises an interrupter in which an interrupting gas in a chamber is heated and resolved by the arc energy in the chamber and the increase in pressure.
The gas increased in pressure is stored in the enclosed space choked with the arc flow and as the arc current decreases, the gas will flow through openings caused by the decreased arc diameter to quench the arc. In this interrupter, however, the gas pressure in the enclosed space will excessively increase due to large arc energy in the range of large arcing currents. This pressure rise is accelerated repeatedly by the increased arc energy caused by the arc voltage pressurizing effect resulting in a rapid increase in the arc energy.
As this arc energy will heat the gas in the arcing space excessively to lower density and accelerate thermal electrolytic dissociation of it, the quenching capability is greatly lowered due to increased degree of gas ionization. In addition, contact members are subjected to excessive erosion.